page_title: Electron-transfer dissociation
section_title: Instrumentation
hierarchical_section_title: Electron-transfer dissociation / Instrumentation
caption_attribution_description: English: Bruker high capacity ion trap mass spectrometer source schematic
context_page_description: Electron-transfer dissociation is a method of fragmenting multiply-charged gaseous macromolecules in a mass spectrometer between the stages of tandem mass spectrometry. Similar to electron-capture dissociation, ETD induces fragmentation of large, multiply-charged cations by transferring electrons to them. ETD is used extensively with polymers and biological molecules such as proteins and peptides for sequence analysis. Transferring an electron causes peptide backbone cleavage into c- and z-ions while leaving labile post translational modifications intact. The technique only works well for higher charge state peptide or polymer ions. However, relative to collision-induced dissociation, ETD is advantageous for the fragmentation of longer peptides or even entire proteins. This makes the technique important for top-down proteomics.The method was developed by Hunt and coworkers at the University of Virginia.
context_section_description: Electron transfer dissociation takes place in an ion trap mass spectrometer with an electrospray ionization source. The first ETD experiments at the University of Virginia utilized a radio frequency quadrupole linear ion trap (LQT) modified with a chemical ionization (CI) source at the back side of the instrument (see diagram at right). Because a spectrum can be obtained in about 300 milliseconds, liquid chromatography is often coupled with the ETD MS/MS. The disadvantage of using LQT is that the mass resolving power is less than that of other mass spectrometers.
  Subsequent studies have tried other instrumentation to improve mass resolution. Having a negative CI source at the back of the instrument interfered with the high-resolution analyzer in LQT-Orbitrap and quadrupole time-of-flight (QTOF), so alternate ionization methods for the radical anions have been introduced.
  In 2006 a group at Purdue University led by Scott McLuckey used a quadrupole/time-of-flight (QqTOF) tandem mass spectrometer with pulsed nano-ESI/atmospheric pressure chemical ionization (APCI) dual ionization source using radical anions of 1,3-dinitrobenzene as the electron donor. Later a lab at the University of Wisconsin adapted a hybrid quadrupole linear ion trap-orbitrap mass spectrometer to use ETD. This method also used a front-end ionization method for the radical anions of 9-anthracenecarboxylic acid via pulsed dual ESI sources.
  As ETD is increasingly popular for protein and peptide structure analysis, implementation on easily available ion-trap mass spectrometers coupled with high resolution mass analyzers continues to evolve.
caption: Bruker high capacity ion trap with ETD (schematic diagram) 
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